1. Field of the Invention
In one of its aspects, the present invention provides a process for forming a minimal headspace pouch containing a flowable material. In another of its aspects, the present invention provides an apparatus for forming a minimal headspace pouch containing a flowable material. In yet another of its aspects, the present invention provides a minimal headspace pouch formed by the process of the present invention.
2. Description of the Prior Art
Flexible Liquid Packaging is used to package many consumer goods, particularly food and beverages, which are often packaged in pouches formed of flexible materials. (The term “Liquid Packaging” is understood by those of skill in the art to refer to both liquids and other flowable materials, as explained further below.) Many products packaged in pouches are particularly sensitive to oxygen degradation. Many products particularly in the food industry require minimal air exposure to protect their flavour, colour, nutritive value, texture and shelf life. Oxygen reacts readily with many components of these products forming so-called “off-flavours” and “off-colours”. Removal of oxygen from the packaging process of many foods allows for extended shelf life with no loss of flavour. In the case of film pouches, as a byproduct of certain preferred forming techniques, oxygen is commonly trapped in a headspace that is created above the product upon pouch formation.
Besides the advantages associated with minimizing oxygen exposure, for certain applications, minimal headspace is required to facilitate pouch insertion into a secondary container; a common packaging arrangement involves inserting a pouch in a cardboard box (the “bag-in-box” principle). A slack pouch is easier to insert into a box and will better form to shape than a puffy pouch (i.e. one with a large air-filled headspace).
Fill reliability or control is important in packaging. In fact, headspace is a common associated effect of techniques used to ensure fill reliability. In many jurisdictions, the advertised product quantity is mandated to be a minimum product quantity. Poor fill accuracy therefore requires that the fill level be set at above the posted product quantity, thereby raising costs. Consequently, while limiting headspace is important, it is also important to have reliable fill control. One known method for minimizing headspace involves filling a tube for making a pouch above the level of the top of the pouch and sealing through the product. This method can suffer from poor fill control. In addition, the product can interfere with seal formation.
Pouches made on vertical form-fill-seal machines are widely used in the Liquid Packaging industry. A typical vertical form-fill-seal machine includes a roll unwind, a forming section where film folds itself vertically, a vertical sealing section and a horizontal sealing section (sealing at the same time the top of a filled pouch and the bottom seal of the next pouch) and a chute and/or discharge conveyor system. At both the vertical and horizontal sealing sections, heat sealing jaws are generally employed to seal the film. Product is supplied through a supply conduit, generally a fill tube, delivering product in the continuous film tube created by the vertical sealing jaws. The vertical form-fill-seal method allows the efficient and effective packaging of foods and other products. Minimizing headspace in pouches made by this method would minimize oxygen degradation, and facilitate use of pouches made by this method in applications that require minimal headspace.
U.S. Pat. No. 5,038,550 to Wirsig et al. teaches a process and apparatus for improving vertical form-fill-seal machines, by minimizing the formation of tucks in the horizontal seals of pouches made on a vertical form-fill-seal machine. Minimizing tucking must be a consideration in any modification to a vertical form-fill-seal machine. In one embodiment, the invention includes a pair of transverse heat sealing jaws; a pair of spreader fingers adapted to be inside the tubular film and to shape the tubular film; and one or two pairs of detucker fingers adapted to act in unison with the transverse motion of the heat sealing jaws, to pinch a longitudinal edge of the tubular film and to urge the pinched tubular film transversely in a direction substantially parallel to the closing surfaces of the jaws and away from the other longitudinal edge of the tubular film.
Generally in operation the continuous film tube of vertical form-fill-seal machines is supplied with product from a product delivery system with continuous or intermittent flow through the supply conduit.
The delivery system may include a balance tank equipped with level control (float, ultrasonic, capacitance, etc.) and a supply conduit with a poppet valve for regulating flow. The machine may also include components for maintaining a constant level of product inside the continuous film tube. Typically, these components include a sensor for determining the level of the product inside the continuous film tube and a control device for controlling the poppet valve regulating the flow of product into the continuous film tube.
Known level sensors include a magnetic float housed inside the continuous film tube, the position of which can be determined by sensors positioned inside or outside the continuous film tube.
Other known sensors exploit the electrical conductivity of the product to create a circuit, whereby the values of electric quantities in the circuit, such as current flow, depend on the level of the product inside the continuous film tube.
U.S. Pat. No. 4,675,660 to Boscolo teaches a level sensor that involves creating energy waves inside a supply conduit using a transducer housed inside a packaging tube and contacting the conduit. The energy waves are transmitted to the product inside the packaging tube, which can then be detected and converted so as to indicate the level of the food product.
European patent 681 961 teaches a level sensor that includes a device for detecting temperature located outside a continuous packaging tube and comprising a number of temperature sensors located successively along the tube. The food product level inside the tube is determined based on the relationship between temperature sensors detecting a surface temperature of the tube affected by the food product, and temperature sensors detecting a surface temperature not affected by the food product.
U.S. Pat. No. 6,684,609 to Bassissi et al. teaches a vertical form-fill-seal machine that has a capacitive level sensor. The capacitive level sensor is positioned outside the continuous film tube facing an end portion of the fill conduit. The sensor and the fill conduit define a capacitive element, whose capacitance depends at least in part on the amount of food product therebetween.
Various methods for reducing headspace in packages are known.
U.S. Pat. No. 6,543,206 to Seward et al. teaches an apparatus and method for evacuating and sealing a pre-formed bag made of a sealable material and containing a comminuted product. The bag is positioned with its open upper end around a sleeve through which a hollow probe can be extended. A pair of jaw members close to form an outer temporary seal above an intermediate region of the bag above the level of the surface of the product in the bag where a permanent seal is to be formed. A pair of lower jaw members close to form an inner temporary seal about a lower region of the bag above the surface of the product. With the probe extended through the sleeve into the bag, the bag is evacuated through the probe. After evacuation is completed and the probe is withdrawn, a pair of sealing members close against the intermediate region of the bag in order to form a permanent seal for the bag.
Similarly, published U.S. patent application 2002/0023410 to Seaward et al. teaches an apparatus and method for sealing a pre-formed bag made of a sealable material and containing a flowable product. The bag is positioned with its open upper end around a sleeve through which a hollow probe can be extended. A pair of upper jaw members close to form an outer temporary seal about an upper region of the bag above the level of the surface of the product in the bag. A pair of lower jaw members close to form an inner temporary seal about a lower region of the bag below the upper and intermediate regions and above the surface of the product. The hollow probe is used to evacuate the bag, and after evacuation is completed and the probe is withdrawn, a pair of sealing members close against the intermediate region of the bag to form a permanent seal. The method further teaches bleeding back a small amount of a desirable material, which may be an inert gas.
European patent application 381 400 teaches a form-fill-seal machine having a constraint chute below the heat sealing jaws of the machine. The constraint chute includes two vertical walls, one of the walls being adapted to move away from the other wall under tension and to return to its original position, the degree of tension and the friction of the walls is sufficient to squeeze the pouch, while permitting the pouch to travel therebetween. The plane of both of the walls is perpendicular to the direction of the closing jaws. This patent teaches sealing the tubular film below the material/air interface when pouches are completely filled (no “headspace”).
U.S. Pat. No. 4,964,259 to Ylvisaker et al. teaches a method of deflating a package of solid goods prior to the time the fill opening is sealed that includes a blast of air against the exterior flexible sidewalls of the package to thereby drive gas from the inside of the package. The blast of air impinges above the upper level of the goods and ceases upon the engagement of the sealing jaws.
U.S. Pat. No. 5,231,817 to Sadler teaches a vertical form-fill-seal machine for making material-filled, slack pouches filled with flowable material, having little or no headspace in the pouches. One jaw of the heat sealing assembly has a jaw wall convex about a vertical axis and located below the heat sealing element. The opposite jaw of the assembly has a jaw wall of an elastomeric sheet stretched under tension and adapted to cooperate with the convex jaw wall. During operation, the jaw walls bias against the material-filled pouch causing air to be expelled from the material and collapsing the tube as the jaws are closed. While this system represents an improvement in the art, there remains a need for a process and apparatus for forming minimal headspace pouches via the vertical form-fill-seal method.
It is an object of the present invention to obviate or mitigate at least one of the above-mentioned disadvantages of the prior art.